The effect of rainfall interception loss by Palm-Oil tree towards flood discharge in Seunagan watershed of Nagan Raya district of Aceh Province

Abstract

Flood discharge comes from the surface run-off affected by factors such as evaporation, evapotranspiration, infiltration and interception. This research aims to predict the magnitude of interception demonstrated by a palm-oil tree and its effects toward flood discharge. This paper covers the calculations for rainfall interception loss by a palm-oil tree, designed areal rainfall, and designed flood discharge. During the calculations, the watershed is divided into two sub-watersheds. Rainfall data were obtained from Meulaboh, Beutong and Alue-Bilie station. Areal rainfall distribution obeys the pattern of Gumbel distribution. Areal rainfall of 100 years returns period for each sub-watershed are 230.81 mm and 197.59 mm before the inclusion of interception effects, while after interception effects are included the areal rainfalls are 152.94 mm and 189.09 mm. The calculated effective rainfall using the SCS (soil conservation service) method where the curve number (CN) before interception effects are 72.19 and 73.15 while 81.54 and 73.99 after the interception is accounted. Flood discharge is calculated using the method of unit hydrograph synthetic SCS. Calculation results show that designed flood discharge of 100 years return period before and after the effects of interception were 3,042.72 m3/s and 2,521.23 m3/s, respectively. It shows that rainfall interception loss by the palm-oil tree can reduce the flood discharge.